Generally, flow in a canal is controlled by vertical lift gates or radial gates. These types of gates in ice areas present freeze-in problems and cannot be operated without special protection or precautions. In some ice ares, ice is encountered in such large quantities that it must be cut and sluiced away. This involves considerable expense and waste of water and energy. In other areas where lesser freezing conditions exist, small amounts of steam or electric heat are provided inside of the gate. This, of course, requires special construction and equipment which is costly to install and to operate as well as to maintain. In some installations an open channel clear of ice is maintained along the upstream face of the gate. This has been accomplished by electric heaters or lamps in reflectors just above the water surface and providing a covering over the heat source. Also air bubble systems to maintain the face of the gate free of ice have been utilized. This method requires the provision of perforated pipes or nozzles installed along the lower upstream face of the gate and supplied with air under pressure. The air bubbles create a circulation of warmer bottom water to the surface which serves to melt the cap ice or at least weaken the cap ice to an extent that the gates can be moved.